In this photo released by South Korean Joint Chiefs of Staff via Yonhap, South Korean and U.S. warships participate in their joint military drills in South Korea's East Sea on Monday, Feb. 4, 2013. South Korean and U.S. troops began naval drills Monday in a show of force partly directed at North Korea amid signs that Pyongyang will soon carry out a threat to conduct its third atomic test. (AP Photo/South Korean Joint Chiefs of Staff via Yonhap) KOREA OUT